Prosthetic devices and bone implants can either be made of resorbable or non-resorbable materials. In particular, current bone graft materials include autografts (bone material obtained from the patient), allografts (cadaver bone and bone material typically obtained from tissue banks); xenografts (bone materials from animals), and a variety of artificial or synthetic bone substitute materials. Such bone substitute materials include materials that are biocompatible with existing bone, tendon, cartilage and ligaments, and may comprise metals, ceramics, or composite materials. Although synthetic materials can be designed to have porous structures that can accommodate de-novo bone in-growth, they are generally considered inadequate as being non-osteoinductive.
The prior art has extracted growth factors from demineralized bone matrix (DBM) to be used as a surface coating or a putty to induce bone growth into implant materials. Demineralized bone matrix (DBM) is a well characterized osteoinductive resorbable material containing growth factors, osteogenic proteins and collagen, which has also been extracted from DBM to be used as a gel coating for implant materials. U.S. Patent Application No. 2003/0044445 discloses a DBM soluble extract of proteins that is dried, reconstituted and then mixed with demineralized bone particles to provide a bone filling material. However, there is no teaching of applying a DBM soluble extract to a porous synthetic implant material where the extract coats within the pores.
Alternatively, U.S. Pat. No. 6,576,249 discloses a method for preparing a bone gel and bone putty by dissolving DBM in water, allowing it to form a gel and mixing it with non-demineralized bone particles to form putty. The '249 patent does not disclose using this material as a coating. The presence of the bone particles in the material would prohibit it from coating the pores of a porous implant material.
U.S. Pat. No. 6,376,573 discloses a porous ceramic implant material of coralline hydroxyapatite having a coating within the pores of the material. The coating however, is used to reinforce the implant material and not to promote bone growth. The coating therefore cannot fill the pores, but must only be on the walls of the pores. This is accomplished by adding the coating as a liquid and then catalyzing the conversion to a polymeric material in situ.
As can be seen, there is a need for a coating material for porous implants that promotes bone growth, allowing the integration of the implant within the patient. It would be desirable for the coating to comprise growth factors, including osteoinductive proteins to promote the bone growth.